Microscope Magnification
Magnification = image size / actual size Re-arrange to find any quantity. Always convert units (1 mm = 1000 μm = 1,000,000 nm).
OCR A Level Biology A H420
🧬 OCR A Level Biology Formula Sheet 2026
All the quantitative formulas, statistical tests and key relationships for OCR A Level Biology A (H420) — modules 2 to 6 — for the 2026 exam series.
Quantitative Biology Statistical Tests Genetics & Ecology H420 Specification
Our formula sheets are free to download — save this one as PDF for offline revision.
Aligned with the latest 2026 syllabus and board specifications. This sheet is prepared to match your exam board’s official specifications for the 2026 exam series.
All H420 Quantitative Biology in One Sheet
OCR A Level Biology A (H420) is increasingly quantitative — microscopy, statistics, Hardy-Weinberg and chi-squared tests are tested across all three papers. This 2026 sheet collects every required formula, test and relationship by module.
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Microscopy magnification and resolution
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Fick's law and exchange surface relationships
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Simpson's, Hardy-Weinberg, χ² and Spearman's tests
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Energy efficiency, GPP/NPP and respiratory quotient
Module 2: Foundations in Biology
Cells, microscopy and surface area to volume.
Resolution
Light microscope ≈ 200 nm ; TEM ≈ 0.2 nm ; SEM ≈ 10 nm Resolution depends on the wavelength of radiation used (electrons << visible light).
Surface Area : Volume
Cube of side a: SA = 6a², V = a³, SA:V = 6/a As size increases, SA:V decreases — large organisms need specialised exchange surfaces. Module 3: Exchange & Transport
Fick's law, mass flow, Bohr shift.
Fick's Law of Diffusion
Rate of diffusion ∝ (surface area × concentration gradient) / diffusion distance Adaptations: alveoli (huge SA, thin wall), villi (long, folded), gills (countercurrent flow).
Cohesion-Tension (Plant Transport)
Water potential gradient drives transpiration: leaf < stem < root < soil (most negative to least negative drives flow upward in xylem) Adhesion to xylem walls + cohesion between water molecules = continuous water column.
Oxygen Dissociation Curve & Bohr Shift
Sigmoidal curve: % saturation of haemoglobin vs partial pressure O₂ Bohr shift
Increased pCO₂ / decreased pH shifts curve right → Hb releases O₂ more readily in respiring tissues Module 4: Biodiversity, Evolution & Disease
Simpson's index, Hardy–Weinberg and immunity.
Simpson's Index of Diversity
D = 1 − Σ (n/N)² n = number of individuals of a species, N = total individuals. Closer to 1 = more diverse.
Hardy–Weinberg Principle
p + q = 1 (allele frequencies) p² + 2pq + q² = 1 (genotype frequencies: homozygous dominant + heterozygous + homozygous recessive) Assumes large population, no mutation, no migration, no selection, random mating.
Immune Response
Primary response: slower, lower antibody concentration ; secondary response: faster, higher peak (memory cells) Vaccination → memory B & T cells without disease symptoms ; herd immunity threshold ≈ 1 − 1/R₀ Module 5: Communication, Homeostasis & Energy
Negative feedback, photosynthesis, respiration and respiratory quotient.
Negative Feedback
Stimulus → receptor → coordinator → effector → response → reverses change Examples: thermoregulation, blood glucose (insulin/glucagon), osmoregulation (ADH).
Kidney Filtration
Ultrafiltration in glomerulus → selective reabsorption in PCT (glucose, amino acids, ions, water) Loop of Henle creates medullary salt gradient; ADH increases collecting duct permeability to water Photosynthesis & Respiration
Photosynthesis
6 CO₂ + 6 H₂O → C₆H₁₂O₆ + 6 O₂ (light + chlorophyll) Aerobic respiration
C₆H₁₂O₆ + 6 O₂ → 6 CO₂ + 6 H₂O (≈ 30–32 ATP) Stages
Glycolysis → link reaction → Krebs cycle → oxidative phosphorylation (ETC) Respiratory Quotient (RQ)
RQ = volume CO₂ produced / volume O₂ consumed Carbohydrate ≈ 1.0 ; lipid ≈ 0.7 ; protein ≈ 0.9 ; > 1.0 indicates anaerobic respiration.
Energy Transfer in Ecosystems
% efficiency
% energy transferred = (energy in tissue / energy available from previous level) × 100% (≈ 10% rule) GPP, NPP
GPP = total energy fixed by producers ; NPP = GPP − R (energy lost in respiration) Module 6: Genetics, Evolution & Ecosystems
Genetic crosses, statistical tests and biotechnology.
Monohybrid & Dihybrid Inheritance
Monohybrid (Aa × Aa)
Phenotype ratio 3 : 1 Dihybrid (AaBb × AaBb)
Phenotype ratio 9 : 3 : 3 : 1 (independent assortment) Codominance / sex linkage
1 : 2 : 1 (codominance) ; sex-linked traits expressed on X chromosome Chi-Squared (χ²) Goodness-of-Fit
χ² = Σ (O − E)² / E Degrees of freedom
df = n − 1 (n = number of categories) Reject H₀ at 5% if χ²_calc > critical value; observed differs significantly from expected.
Spearman's Rank Correlation
rₛ = 1 − (6 Σ d²) / (n (n² − 1)) d = difference between paired ranks ; n = number of pairs ; rₛ near +1 / −1 = strong correlation.
Allele Frequency Change (Evolution)
Selection alters p, q over generations: p_new = (p × W_AA × p + W_Aa × q) / W̄ where W̄ = mean fitness Genetic drift is more pronounced in small populations; bottleneck effect reduces variation.
Gene Therapy & Biotechnology
PCR cycles: denaturation 95°C → annealing 50–65°C → extension 72°C ; amplifies DNA exponentially (2ⁿ copies after n cycles) Recombinant DNA: cut with restriction enzymes (sticky ends) → ligate with DNA ligase → insert into vector → transform host How to Use This Formula Sheet
Boost your Cambridge exam confidence with these proven study strategies from our tutoring experts.
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Drill the Statistical Tests
OCR routinely tests χ², Spearman's rank, Simpson's index and Hardy-Weinberg with full calculations — practise from raw data through to a written conclusion.
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Convert Microscopy Units Carefully
Magnification questions involve μm, nm and mm. Always write units explicitly and convert before substituting to avoid easy mark losses.
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Master the 6-Mark Mechanisms
Synoptic 6-mark questions on photosynthesis, respiration, neuron impulses or kidney function need clear, sequenced reasoning. Practise writing them in 6-8 minutes.
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Define Key Terms Precisely
OCR mark schemes reward exact biological vocabulary — e.g. 'water potential', 'osmosis', 'specific immune response'. Always use the syllabus term, not a paraphrase.
Formula Sheet FAQ
Quick answers about this free PDF and how to use it for exam revision and active recall.
Is the OCR A Level Biology Formula Sheet 2026 free to download as a PDF?
Yes. This Tutopiya formula sheet is free to use and you can download it as a PDF from this page for offline revision. There is no payment or account required for the PDF download.
What Biology topics and equations does this formula sheet cover?
This page groups key Biology formulas in one place for revision. OCR A Level Biology A (H420) formula sheet for 2026: microscopy, Fick's law, Simpson's index, Hardy-Weinberg, χ² goodness-of-fit, Spearman's rank, energy efficiency and more. Always cross-check with your official syllabus and past papers for your exam session.
Can I use this instead of the official exam formula booklet in the exam?
No. In the exam you must follow only what your exam board allows in the hall—usually the official formula booklet or data sheet where provided. This page is a revision and teaching aid, not a replacement for board-issued materials.
Who is this formula sheet for (Upper Secondary)?
It is written for students preparing for assessments at Upper Secondary in Biology, including classroom revision, homework support, and independent study. Teachers and tutors can also share it as a quick reference.
How should I revise with this formula sheet?
Work through past paper questions, quote the correct formula before substituting values, and check units and notation every time. Pair this sheet with timed practice and mark schemes so you see how examiners expect working to be set out.
Where can I get more help with Biology revision?
Explore Tutopiya’s study tools, past paper finder, and revision checklists linked from our tools hub, or book a trial lesson with a subject specialist for personalised support alongside this formula reference.
Need Help with OCR A Level Biology?
Tackle quantitative biology, statistical tests and 6-mark synoptic questions with an experienced OCR A Level Biology tutor. We focus on H420 specification content, exam phrasing and mark scheme expectations.
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This formula sheet aligns with OCR A Level Biology A (H420) for the 2026 exam series.
OCR provides a Data Sheet in the exam — check the latest specification to confirm which formulas (e.g. Simpson's, Hardy-Weinberg) are given vs which must be memorised.